1. Field of the Invention
The present invention relates to an eyepiece, and more particularly to an eyepiece used in telescopes, microscopes, etc.
2. Related Background Art
In general, in order to facilitate observation of the field in an eyepiece from the center to the periphery thereof, an eye relief (an axial distance between a most-eye-side lens surface of the eyepiece and the eye point) is desired to be at least 80% of a focal length of the eyepiece. It is, however, well known that the eye relief becomes shorter as an apparent field of view increases while keeping aberrations of marginal rays of the eyepiece in a certain state. It is also well known that in order to increase the eye relief without decreasing the apparent field of view, it is necessary to increase the size of an aperture of an eye-side lens system. This, however, results in drastic deterioration of aberrations of marginal rays, astigmatism and distortion in particular.
As described above, conventional eyepieces had a problem that it was very difficult to secure a wide apparent field of view and a long eye relief at a time while correcting aberrations well.